source: trunk/FACT++/erfa/src/s06a.c@ 20000

Last change on this file since 20000 was 18921, checked in by tbretz, 8 years ago
Updated to ERFA 1.4.0
File size: 6.2 KB
Line 
1#include "erfa.h"
2
3double eraS06a(double date1, double date2)
4/*
5** - - - - - - - -
6** e r a S 0 6 a
7** - - - - - - - -
8**
9** The CIO locator s, positioning the Celestial Intermediate Origin on
10** the equator of the Celestial Intermediate Pole, using the IAU 2006
11** precession and IAU 2000A nutation models.
12**
13** Given:
14** date1,date2 double TT as a 2-part Julian Date (Note 1)
15**
16** Returned (function value):
17** double the CIO locator s in radians (Note 2)
18**
19** Notes:
20**
21** 1) The TT date date1+date2 is a Julian Date, apportioned in any
22** convenient way between the two arguments. For example,
23** JD(TT)=2450123.7 could be expressed in any of these ways,
24** among others:
25**
26** date1 date2
27**
28** 2450123.7 0.0 (JD method)
29** 2451545.0 -1421.3 (J2000 method)
30** 2400000.5 50123.2 (MJD method)
31** 2450123.5 0.2 (date & time method)
32**
33** The JD method is the most natural and convenient to use in
34** cases where the loss of several decimal digits of resolution
35** is acceptable. The J2000 method is best matched to the way
36** the argument is handled internally and will deliver the
37** optimum resolution. The MJD method and the date & time methods
38** are both good compromises between resolution and convenience.
39**
40** 2) The CIO locator s is the difference between the right ascensions
41** of the same point in two systems. The two systems are the GCRS
42** and the CIP,CIO, and the point is the ascending node of the
43** CIP equator. The CIO locator s remains a small fraction of
44** 1 arcsecond throughout 1900-2100.
45**
46** 3) The series used to compute s is in fact for s+XY/2, where X and Y
47** are the x and y components of the CIP unit vector; this series is
48** more compact than a direct series for s would be. The present
49** function uses the full IAU 2000A nutation model when predicting
50** the CIP position.
51**
52** Called:
53** eraPnm06a classical NPB matrix, IAU 2006/2000A
54** eraBpn2xy extract CIP X,Y coordinates from NPB matrix
55** eraS06 the CIO locator s, given X,Y, IAU 2006
56**
57** References:
58**
59** Capitaine, N., Chapront, J., Lambert, S. and Wallace, P.,
60** "Expressions for the Celestial Intermediate Pole and Celestial
61** Ephemeris Origin consistent with the IAU 2000A precession-
62** nutation model", Astron.Astrophys. 400, 1145-1154 (2003)
63**
64** n.b. The celestial ephemeris origin (CEO) was renamed "celestial
65** intermediate origin" (CIO) by IAU 2006 Resolution 2.
66**
67** Capitaine, N. & Wallace, P.T., 2006, Astron.Astrophys. 450, 855
68**
69** McCarthy, D. D., Petit, G. (eds.), 2004, IERS Conventions (2003),
70** IERS Technical Note No. 32, BKG
71**
72** Wallace, P.T. & Capitaine, N., 2006, Astron.Astrophys. 459, 981
73**
74** Copyright (C) 2013-2017, NumFOCUS Foundation.
75** Derived, with permission, from the SOFA library. See notes at end of file.
76*/
77{
78 double rnpb[3][3], x, y, s;
79
80
81/* Bias-precession-nutation-matrix, IAU 20006/2000A. */
82 eraPnm06a(date1, date2, rnpb);
83
84/* Extract the CIP coordinates. */
85 eraBpn2xy(rnpb, &x, &y);
86
87/* Compute the CIO locator s, given the CIP coordinates. */
88 s = eraS06(date1, date2, x, y);
89
90 return s;
91
92}
93/*----------------------------------------------------------------------
94**
95**
96** Copyright (C) 2013-2017, NumFOCUS Foundation.
97** All rights reserved.
98**
99** This library is derived, with permission, from the International
100** Astronomical Union's "Standards of Fundamental Astronomy" library,
101** available from http://www.iausofa.org.
102**
103** The ERFA version is intended to retain identical functionality to
104** the SOFA library, but made distinct through different function and
105** file names, as set out in the SOFA license conditions. The SOFA
106** original has a role as a reference standard for the IAU and IERS,
107** and consequently redistribution is permitted only in its unaltered
108** state. The ERFA version is not subject to this restriction and
109** therefore can be included in distributions which do not support the
110** concept of "read only" software.
111**
112** Although the intent is to replicate the SOFA API (other than
113** replacement of prefix names) and results (with the exception of
114** bugs; any that are discovered will be fixed), SOFA is not
115** responsible for any errors found in this version of the library.
116**
117** If you wish to acknowledge the SOFA heritage, please acknowledge
118** that you are using a library derived from SOFA, rather than SOFA
119** itself.
120**
121**
122** TERMS AND CONDITIONS
123**
124** Redistribution and use in source and binary forms, with or without
125** modification, are permitted provided that the following conditions
126** are met:
127**
128** 1 Redistributions of source code must retain the above copyright
129** notice, this list of conditions and the following disclaimer.
130**
131** 2 Redistributions in binary form must reproduce the above copyright
132** notice, this list of conditions and the following disclaimer in
133** the documentation and/or other materials provided with the
134** distribution.
135**
136** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
137** the International Astronomical Union nor the names of its
138** contributors may be used to endorse or promote products derived
139** from this software without specific prior written permission.
140**
141** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
142** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
143** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
144** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
145** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
146** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
147** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
148** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
149** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
150** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
151** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
152** POSSIBILITY OF SUCH DAMAGE.
153**
154*/
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